The invention concerns an assembly to wind-unwind thin slabs.
The winding-unwinding assembly according to the invention is installed advantageously downstream of continuous casting plants producing thin slabs or downstream of roughing rolling mill stands.
This winding-unwinding assembly is employed to wind thin slabs leaving a continuous casting plant, or leaving the temperature-equalisation furnace downstream of continuous casting plants producing thin slabs, or leaving a roughing rolling mill stand and has the task of forming coiled rolls of slab which are uncoiled thereafter for use in the successive rolling operations.
U.S. Pat. No. 4,630,352 discloses a winding-unwinding assembly in which the thin slab leaving a continuous casting plant is caused to cooperate with a temperature-equalisation furnace before cooperating with the winding-unwinding assembly.
This winding-unwinding assembly comprises two substantially horizontal winding-unwinding drums, the axes of rotation of which are arranged on a substantially vertical plane perpendicular to the direction of feed of the thin slab.
These two drums are positioned respectively above and below the plane of feed of the thin slab to be wound-unwound and cooperate advantageously with burners which keep the temperature of the slab at a pre-set value.
A movable guide table is fitted in the space between the respective upper and lower drums and is positioned substantially on the same plane as the plane of feed of the thin slab. This movable guide table directs the thin slab upwards or downwards as required for the winding of the thin slab on the upper or lower drum respectively.
At least one rolling mill stand is installed downstream of the winding-unwinding assembly.
In this way, while one thin slab is being coiled on one of the two winding-unwinding drums, the thin slab already coiled on the other winding-unwinding drum is unwound and caused to cooperate with the rolling mill stand and is then wound onto an auxiliary winding-unwinding drum positioned downstream of the rolling mill stand.
By making the thin slab pass through the rolling mill stand a desired number of times in both directions from the aforesaid other winding-unwinding drum to the auxiliary winding-unwinding drum and back again, it is possible to produce a coiled roll of sheet of the required thickness.
This embodiment requires that one of the two winding-unwinding drums should be positioned below the plane of the feed of the thin slab and thus entails considerable excavation and building operations.
EP-A-0321733 too discloses a winding-unwinding assembly in which two winding-unwinding units are positioned substantially vertically opposite each other; this lay-out entails very high costs for the excavation operations required.
GB-B-1,075,789 discloses a winding-unwinding assembly in which two winding-unwinding drums are arranged diametrically opposite to each other on a substantially horizontal rotary platform. Each winding-unwinding drum is fitted onto an underlying saddle, which can move vertically to suit the various dimensions of the coils being formed.
Furthermore, the winding-unwinding drums comprise a shaft which can be extended lengthwise and on which is installed a means to expel the coil, which is engaged by a loading arm positioned laterally on the same axis as one of the winding-unwinding drums; the winding assembly disclosed is somewhat complex.
The state of the art contains also cradle-type winding-unwinding assemblies, in which the coiled roll of thin slab is taken from its supporting cradle and is discharged onto an unwinding cradle. This embodiment requires means to handle the wound rolls and therefore becomes very complicated and necessitates a considerable financial investment.
WO-A-8908512 discloses a winding-unwinding assembly in which two winding-unwinding units are solidly fitted to a rotary platform and are contained within a chamber solidly installed above the rotary platform. The chamber includes two lateral openings arranged respectively opposite to each other along the axis of feed of the slab so as to enable the slab being wound to enter at one side and the slab being unwound to emerge at the other side.
These openings are very high so as to make possible the operations of winding and unwinding the slab and therefore lead to a great loss of heat from the slab, which has to be heated within the chamber so that its temperature can be kept at a pre-set value. Moreover, the chamber includes a stationary intermediate wall which separates the winding unit from the unwinding unit, thus making impossible the elimination of the operation of winding/unwinding the slab even when the rolling line downstream of the winding-unwinding assembly travels at the same speed as the continuous casting plant feeding the winding-unwinding assembly.
Moreover, in the winding-unwinding assembly disclosed the pairs of rolls drawing the slab entering or leaving the winding-unwinding assembly are positioned outside the chamber, with a resulting further loss of heat from the thin slab being processed.
The present applicants have designed, tested and embodied this invention to overcome the shortcomings of the state of the art, as requested by users for some time now, and to achieve further advantages.